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Abstract: Silkworms have been developed over thousands years to optimize folding and crystallization of fibroin under highly controlled conditions which have resulted in their efficient fiber formation. In this paper, we reconstructed the three-dimensional architecture of the spinneret of a wild silkworm Samia cynthia ricini from approximately 1000 optical micrographs of the semi-thin cross sections. The chitin plates and muscles were observed in the silk press part together with large change in the diameter of the spinneret lumen at the press part by large shear stress. This is similar to the case of the spinneret of Bombyx mori silkworm, indicating that the structural change in the silk fibroin of S.c. ricini silkworm occurs exclusively at the silk press part due to large shear stresses. Molecular dynamics (MD) calculations were then performed to study the structural change that occurs in the crystalline region of S.c. ricini silk fibroin under shear stress. Namely, using the peptide AGGAGG(A)12GGAGAG as a model of the crystalline part of the silk fibroin under different shear stresses in the presence of water molecules and followed by molecular mechanics (MM) calculation after removal of water molecules. The simulation indicates that the Ala residues in the model peptides adopt a predominantly β-sheet structure under shear stresses of above 1.0GPa. [Copyright &y& Elsevier]

A new solid-state NMR experimental equipment was developed to monitor the structural change of polymer and protein fibers under active uniaxial deformation. The equipment was applied to monitoring change in the structure of a biodegradable aliphatic polyester fiber, poly(tetramethylene succinate) (PTMS; [–O(CH 2 ) 4 OCO–(CH 2 ) 2 CO–] n ), as a function of tensile stress. The crystal transition from α to β forms for PTMS was induced by stress and monitored by the change of the methylene region in the 13 C NMR spectra. The 13 C chemical shielding constant for the model compound of poly(tetramethylene succinate) was calculated using the GIAO–CHF (gauge invariant atomic orbitals–coupled Hartree–Fock) with ab initio 6-311G ∗∗ basis set. This calculation acceptably explains the experimental results. [ABSTRACT FROM AUTHOR]

The properties of polyglycolide (PGA) fibers used as surgical sutures depend on their aggregated state structure. The study investigated the relationship between the structural evolution and macroscopic properties of PGA fibers with low-crystallinity under coupled stress-temperature fields by conducting in-situ WAXD/SAXS, DSC and SEM measurements. The WAXD and SAXS results indicated that the structural evolution during the low-temperature stretching stage primarily relied on stress-induced amorphous molecular chain orientation and the formation of small crystals. The DSC results confirmed that uniaxial stretching enhanced the orientation of amorphous molecular chains, leading to cold crystallization of PGA fibers at lower temperatures. During the heating stretching stage at temperatures of 60–90 °C, numerous crystals were generated through a lamellar insertion mechanism and underwent lateral growth. This is reflected by the crystallinity, crystal orientation, and crystallite sizes increased significantly, while the long period decreased rapidly. The high-temperature stretching stage resulted in fragmentation and recrystallization of lamellar crystals, forming fibrous crystals. Stretching at 110 °C exhibited higher Iq 2 /Iq 1 values than other temperatures, which means that 110 °C is more favorable for the formation of fibrous crystals. Additionally, PGA fibers stretched at 150 °C exhibited the highest crystallinity and crystal orientation, which led to a 440 % increase in tensile strength. Its resistance to degradation has also been significantly improved compared to the original fibers. [Display omitted] • Low-crystallinity PGA fibers were stretched during variable temperature. • The stress and temperature fields dominated the structural evolution in different stretching stages. • Hot stretching improved the mechanical properties and resistance to degradation of PGA fibers. [ABSTRACT FROM AUTHOR]

Many gel-like soft composites were obtained by using thermoplastic polyurethane (TPU) as the matrix in this work. Different contents of plasticizer dibutyl adipate (DBA) was added to TPU to swell its molecular chains and allowed them to pass through each other easily. These samples were then sandwiched between two electrodes as actuators and their actuation abilities were investigated. The results showed that the largest deflection among those samples was up to 12.11 mm, which corresponds to 48.44% of the length of samples (at 2.86 V μm−1). The deflection increased with increasing of the electric field intensity. Besides, the actuator was able to promptly respond to the change of voltage within 0.12 s. A wide response ability in the frequency region from 0.5 Hz to 10 Hz was confirmed, and the largest amplitude over 22 mm of the actuator was observed at 5 Hz. Furthermore, a new method was proposed in this paper to estimate the tiny force generated by the actuator. The small variation (less than 3%) of the measured results indicated that the proposed method is reliable even at a small bending angle. It is believed that the rapid bending capability and large deformation of the developed actuator at low intensity of electric field will make its considerable contributions to the field of soft robotics or biomaterials. Image 1 • Plasticized gel based actuators were prepared and their properties were investigated. • The largest actuating deflection was up to 48.44% of the sample length at 2.86 V μm−1 • The actuation behaviors in an electric field is a consequence of multiple factors. • A new method was proposed to estimate the tiny actuation force. [ABSTRACT FROM AUTHOR]

Phase change fibers (PCFs) as a kind of composite material, the composition and spatial distribution of each phase have a great influence on its thermal and mechanical properties. In this article, PCFs with polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB), and polyacrylonitrile (PAN) as sheath and 30% octadecane kerosene as core were prepared by coaxial electrospinning. It was found that octadecane had the highest supercooling degree when it was encapsulated in PVB. Thus, we used pure octadecane, 30% octadecane of isopropanol, chloroform, and kerosene solutions as core solutions, adjusted the fine structure of octadecane in PVB sheath, and four kinds of PCFs with different octadecane particle size and spacing were prepared. Successfully reduced the supercooling degree of octadecane. To compare the mechanical properties of the four fibers. It was found that the composite fiber obtained by using isopropanol as octadecane solvent had the most comprehensive mechanical performance. To find a universal method to control the distribution structure of phase change materials (PCMs) in fibers by coaxial electrospinning, we used PAN and PVDF as the sheath solution, pure octadecane, 30% octadecane in isopropanol, chloroform, petroleum ether, and kerosene solutions as a core solution to prepare the PCFs. Characterization results and analysis of the properties of solutions showed that only when the viscosity of the core and sheath solution was relatively low, it could obtain the bamboo-like structured fibers. And continuous core-sheath structured fibers could be obtained in two situations. First, the low viscosity of sheath solution and high viscosity of core solution; second, the high viscosity of sheath solution. [Display omitted] • Successfully prepared phase change fibers with different internal structures. • Optimize core distribution can suppress supercooling. • Optimize core distribution can improve mechanical properties. • Adjusting the solution viscosity can change the internal structure of the fiber. [ABSTRACT FROM AUTHOR]

Stable energy storage materials have become the research focus today. Coaxial electrospinning can prepare core-sheath nanofibers loaded with phase change materials (PCMs). This method requires the sheath solution have good spinnability and encapsulation ability. Suitable solutions can be prepared by the thermal cross-linking method to improve the properties of nanofibers. Choose hexamethylene diisocyanate (HDI) and β-cyclodextrin (β-CD) as cross-linking agents to adjust the performance of polyvinyl butyral (PVB)/N, N-dimethylformamide (DMF) solution. The adjustment of β-CD addition amount and thermal cross-linking time prepared the best sheath solution as PVB/50CD/HDI. The latent heat of nanofibers prepared by using this sheath solution could be as high as 137.05 J/g. In the meantime, the properties of nanofibers in thermal decomposition, mechanical strength, and elongation rate were also improved. The thermal cycle test proved the good stability of core-sheath nanofibers. This work lays the foundation for the further development of temperature-regulating fibers with high latent heat and performance. [Display omitted] • The core-sheath nanofibers with high latent heat were successfully prepared. • The thermal cross-linking has a good auxiliary effect on coaxial electrospinning. • It has good applications in energy storage systems and thermal regulating garments. [ABSTRACT FROM AUTHOR]